Fixing device and image forming apparatus using the same

Abstract: A fixing device (35) includes fixing and pressure rollers (13, 15) rotatably supported by the frame (39), and a compressible cleaning pad (47) supported by a holder (45), which is inserted into and engaged with the frame (39). The cleaning pad (47) is in contact with a fixing surface (13b) of the fixing roller (13) such that the cleaning pad (47) is not compressed when the fixing roller (13) is not rotated and is compressed to effect the cleaning operation when the fixing roller (13) is rotated.

Description: This invention relates to a fixing device and an electrographic image forming apparatus according to the preamble of claims 1 and 6. In particular, the invention relates to a fixing device, which is used in an image forming apparatus to fix a toner image on a paper sheet, including a fixing roller, a pressure roller engaged with the fixing roller and a cleaning pad which is in contact with the surface of the fixing roller to clean the surface of the roller. As is well known, a conventional image forming apparatus, e.g., electro-photo copying machines, laser beam printers, etc., typically includes an image forming unit for forming an image on an image carrier, a developing unit for developing the image, as a visible image, on the image carrier by a toner powder, and a transfer unit for transferring the developed image formed on the image carrier to a paper sheet. The image forming apparatus also includes a fixing unit which fuses the toner powder (developed image) on the paper sheet and fixes the fused toner on the paper sheet as a fixed image. A conventional fixing unit is shown in FIGURE 1. A fixing unit 11 includes a cylindrical fixing roller (heat roller) 13 in which a heater (not shown) is provided at a center portion along a length thereof. Each side of fixing roller 13 is rotatably supported by a suitable bearing means, respectively, and fixing roller 13 is rotated in counter-clockwise by a motor (not shown). A pressure roller 15 is located below fixing roller 13 such that it is forcibly engaged with the surface of fixing roller 13 by a spring (not shown). Thus, pressure roller 15 is rotated clockwise when fixing roller 13 is rotated as described above. As shown in FIGURE 1, those rollers 13 and 15 are rotatably located in a housing 17. A lead-in opening 17a is opened in one side wall of housing 17 to introduce a paper sheet P into housing 17 and a lead-out opening 17b is also opened in the opposite side wall to discharge paper sheet P from housing 17. A cleaning unit 18 is slidably fitted in an opening 21 formed in the upper wall of housing 17. Cleaning unit 18 has a cleaning pad 19 therein. One end of pad 19 is in contact with the surface of fixing roller 13 at a prescribed pressure by a suitable pressing means, e.g., a leaf spring 23. One end of leaf spring 23 is fixed to an upper openable cover 25 of an image forming apparatus and the other end is in contact with cleaning unit 18 to urge cleaning pad 19 on the surface of fixing roller 13. Leaf spring 23 has relatively a long length to easily regulate the pressure on cleaning pad 19. Cleaning pad 19 is always urged on the surface of fixing roller 13 under the prescribed pressure. A paper sheet P on which a developed toner image has been transferred is led into fixing unit 11 (housing 17) through lead-in opening 17a. When paper sheet P passes through the contact portion between fixing roller 13 and pressure roller 15, the toner on paper sheet P is fused by heat and pressure generated by rollers 13 and 15 and is fixed on paper sheet P as a fixed image. In this fixing operation, almost all fused toner is fixed on paper sheet P, but a part of fused toner on the surface of paper sheet P may be transferred to the circumferential surface of fixing roller 13. The transferred toner on fixing roller 13 is removed by cleaning pad 19. There is a tendency to minimize the external size of an image forming apparatus. Thus, a compact size, in particular a reduced height of the fixing unit is desired to achieve a reduced external size of the image forming apparatus. In the conventional fixing unit having the above-described construction, it may be difficult to reduce the height of the unit because of the leaf spring. If the length of the leaf spring 23 is reduced, regulation of pressure generated by the leaf spring 23 may be difficult. If the pressure applied by the leaf spring 23 to the cleaning pad 19 is too great, this results in the reduction of durability of the cleaning pad 19. Conversely, if the pressure applied is too low, insufficient cleaning by the cleaning pad may occur. Since the cleaning pad 19 of the conventional fixing unit is always urged on to the surface of the fixing roller 13 at a prescribed pressure, the cleaning pad 19 may be deformed, and the service life of the cleaning pad 19 shortened. Patent Abstracts of Japan vol. 14 no. 150 (P-1025) (4093) and JP-A-2 12 182 discloses a wiping assembly for a heat roller in which the wiping element is elastically pressed against the roller when an access cover is in a closed position, and is released when the access cover is in an open position. IBM Technical Disclosure Bulletin vol. 25 no. 3B page 1355-1356 discloses a wedge-shaped block, placed between a frame and the surface of a roller, which has abrasive material on its surface so as to automatically roughen and clean the surface of the roller. According to a first aspect of the present invention, there is provided a fixing device which receives a medium (P) on which a toner image is supported, comprising: a frame; an elongated fixing roller rotatably supported by the frame; an elongate pressure roller rotatably supported by the frame and forcibly engaged with the fixing roller to carry out a fixing operation in which the toner on the medium (P) is fixed; an elongate cleaning holder detachably located in the frame; and a compressible cleaning pad supported by the holder, characterised in that: one elongated surface of the holder is inclined with respect to the horizontal elongated surface of the holder; in that the cleaning pad is supported by the inclined surface of the holder, such that the surface of the cleaning pad is in contact with a portion of the surface of the fixing roller at a first position offset from the position on the surface of the fixing roller intersected by a vertical line (VL) passing through the rotational centre (13r) of the fixing roller; and in that loading means are provided for performing an engagement of the cleaning holder and the frame only when said fixing roller is rotated during a fixing operation such that the holder is located at a position in the frame in which the cleaning pad is moved to a cleaning position where it is forcibly compressed against the surface of the fixing roller at said second cleaning position. The fixing unit according to the invention enables improved service life of the cleaning unit by having a self-loading mechanism. This also enables a reduction in the number of components of the fixing device and enables reduction in height of an image forming apparatus using the fixing device, when compared with a conventional image forming apparatus. According to a second aspect of the present invention, there is provided an electrographic image forming apparatus comprising: image forming means for forming a toner image on a medium (P); a frame; an elongated fixing roller rotatably supported by the frame; an elongated pressure roller rotatably supported by the frame and forcibly engaged with the fixing roller to carry out a fixing operation in which the toner image is fixed on the medium (P); an elongate cleaning holder detachably inserted in the frame; and a compressible cleaning pad supported by the holder detachably inserted in the frame, characterised in that one elongated surface of the holder is inclined with respect to the horizontal elongated surface of the holder, and in that the cleaning pad is supported by the inclined surface of the holder so that the surface of the cleaning pad is in contact with a portion of the surface (13b) of the fixing roller at a first position offset from the position on the surface of the fixing roller intersected by a vertical line (VL) passing through the rotational centre (13r) of the fixing roller, and in that loading means are provided for performing an engagement of the cleaning holder and the frame only when said fixing roller is rotated during a fixing operation such that the holder is located at a position in the frame in which the cleaning pad is moved to a cleaning position in which it is forcibly compressed against the surface of the fixing roller at said second cleaning position. For a better understanding of the present invention and to show more clearly how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which:- FIGURE 1 is a schematic view illustrating a conventional fixing device; FIGURE 2 is a schematic side view illustrating a printer including a fixing device of one embodiment of the present invention; FIGURE 3 is an enlarged and partly sectional schematic view of the fixing device shown in FIGURE 2; FIGURE 4 is an enlarged perspective view illustrating the fixing device shown in FIGURE 2; FIGURE 5 is an exploded view of the fixing device shown in FIGURE 4; FIGURE 6 is an enlarged perspective view of a cleaning unit of fixing device shown in FIGURES 4 and 5; FIGURE 7 is a view illustrating the operational idea of the cleaning unit of the fixing device shown in FIGURE 3; and FIGURE 8 is a schematic view illustrating a modification of a fixing device of the present invention. An embodiment of the present invention will now be described with reference to FIGURE 2 through FIGURE 7. In the embodiment, a fixing device of the present invention is applied to a well known laser beam printer. As shown in FIGURE 2, a laser beam printer 31 includes an image forming unit 33 and a fixing device 35. Image forming unit 33 typically includes an image carrier, a charger, a laser beam exposure device, a developing device and a transfer device. The image forming unit 33 may include a cleaning device, if needed. Respective devices of image forming unit 33 are well known in the art, and therefore they are not shown in FIGURE 2 for the purpose of simplicity. A detailed operation of each device of image forming unit 33 also is not described. In FIGURE 2, image forming unit 33 forms a latent image on the image carrier by the laser beam exposure device and develops the latent image, as a toner image, by the developing device. Image forming device 33 transfers the toner image by the transfer device from the image carrier to a paper sheet P fed from a paper tray 36. Then, paper sheet P on which the toner image is transferred is further fed to fixing device 35. The toner image is fixed on paper sheet P by fixing device 35 and paper sheet P is then discharged from laser beam printer 31. A detail construction of fixing device 35 will be described by referring FIGURES 3, 4, 5 and 6. As shown in FIGURES 3 and 5, a fixing roller 13 is disposed in a housing 37 of fixing device 35 and rotatably supported by a frame 39 shown in FIGURE 5. Fixing roller 13 includes an elongated metallic hollow sleeve 13a in which a heating lamp 14 is disposed, as a heating source, along the axial direction thereof. Other heating source may be located in sleeve 13a, instead of the heating lamp. A circumferential surface of sleeve 13a is provided with a silicon rubber layer 13b which acts as a fixing surface. A pressure roller 15 is also rotatably supported by frame 39 so that the circumferential surface of pressure roller 15 is forcibly engaged with the surface of fixing roller 13, as shown in FIGURE 3. Thus, pressure roller 15 is dependently rotated as fixing roller 13 is rotated by a suitable driving source, e.g., motor, in a direction indicated by an arrow R. As shown in FIGURE 3 and 5, an elongated opening 41 through which a cleaning unit 42 is inserted is provided in frame 39. Opening 41 is formed so that it is located at a portion offset by a prescribed amount from the vertical line VL passing through the rotational center 13r of fixing roller 13. As can be seen in FIGURE 3, opening 41 is offset to the paper lead-out side of fixing roller 13. A pair of inner projections 39a and 39b is formed at opposite inner sides of frame 39 to engage with a pair of short projections 43a and 43b formed at opposite side walls 45a and 45b of an elongated holder 45 of cleaning unit 42, respectively. As can be seen in FIGURE 6, a plate shaped elongated and compressible cleaning pad 47 made of felt is firmly supported by holder 45. A lower surface of holder 45 to be opposite to the surface of fixing roller 13 is slanted and a recess 48 is formed therein. One surface of cleaning pad 47 may be grooved into recess 48 and fixed on the lower surface of holder 45 with a suitable adhesive. Thus, the other surface of cleaning pad 47 is also slanted against the horizontal level. A pair of handles 49 projects from an upper surface of holder 45 to easily insert holder 45 into opening 41 of frame 39. The pair of handles 49 is located at an off-center portion of holder 45 near side wall 45b. A leaf plate 51 one end of which is fixed to side wall 45a of holder 45 is extended along the side wall 45a to generate a suitable resilient force. Leaf plate 51 with a suitable resilient force prevents holder 45 from undesirable moving and maintains the engagement between holder 45 and frame 39 when holder 45 is located at a prescribed position in opening 41. As similar to the conventional fixing device shown in FIGURE 1, a paper lead-in side 53a and a paper lead-out side 53b is defined in the corresponding front and rear sides of frame 39 (fixing device 35), respectively. A pair of paper feed roller units 55a and 55b is rotatably disposed at paper lead-in side 53a of fixing device 35, as shown in FIGURE 4. Conventional temperature detectors (thermistor, thermostat and thermal fuse) are also provided in fixing device 35 to detect temperature of fixing roller 13. Undesirable temperature rise of fixing roller 13 is avoided by the detectors. When cleaning unit 42 is inserted into opening 41 of fixing device 35, an operator pinches the pair of handles 49 and inserts it into opening 41. Firstly, one of the short projections 43a of side wall 45a is inserted below the rear surface of inner projection 39a. Then, holder 45 is rotated around the engaged portion of projection 43a and inner projection 39a so that the other end of holder 45 is inserted into opening 41. The other short projection 43b of side wall 45b is also inserted below the rear surface of the corresponding inner projection 39b. As shown in FIGURES 3 and 4, the other surface of cleaning pad 47 is in contact with the circumferential surface of fixing roller 13 by the gravity of cleaning unit 42 and holder 45 is located at the prescribed position in opening 41. In more detail, the other surface of cleaning pad 47 is in contact with a portion of the surface of fixing roller 13 located on an ideal line N, passing through rotational center 13r of fixing roller 13, which has a prescribed angle , e.g., 33° , against perpendicular line VL in a counter clockwise direction in FIGURE 3. In addition, holder 45 is engaged with the inner surface of frame 39 at a down stream side from the contacting portion between cleaning pad 47 and fixing roller 13 in a rotational direction (clockwise direction) of fixing roller 13 indicated by an arrow R. Ideal line N and the surface of cleaning pad 47 is intersected with each other at substantially right angles so that the contact area between cleaning pad 47 and the surface of fixing roller 13 is maximized. Thus, toner remaining on the surface of fixing roller 13 is effectively removed by cleaning pad 47. In this position, undesirable movement of holder 45 is avoided by the resilient force of leaf plate 51 of holder 45, which is engaged with the top of inner projection 39a. The engagement between holder 45 and frame 39 is also maintained. In this state, holder 45 and frame 39 may be loosely engaged with one the other when fixing roller 13 is not rotated. In the above-described construction, the extending end of the pair of handles 49 of holder 45 may be formed obliquely in conformity with the shape of an upper cover of the apparatus. A theory of operation of the above-described fixing device 35 will now be described with reference to FIGURE 7. In a first position indicated by a solid line in FIGURE 7, cleaning pad 47 is not compressed and thus the cleaning operation is not effected. When fixing roller 13 is rotated by a motor (not shown) in the direction indicated by an arrow R, cleaning pad 47 of cleaning unit 42 is urged by a frictional force F generated between the surface of fixing roller 13 and cleaning pad 47 toward the rotational direction R of fixing roller 13. Cleaning pad 47 is rotated around the pair of inner projections 39a and 39b of frame 39 where the pair of short projections 43a and 43b of holder 45 is engaged with the pair of inner projections 39a and 39b, respectively. Cleaning pad 47 is sagged and deformed and is moved along the surface of fixing roller 13 to a second position as indicated by a phantom line in FIGURE 7. Thus, cleaning pad 47 is compressed by a contracted amount ΔL and presses the surface of fixing roller by an elastic restoring force thereof corresponding to the contracted amount ΔL. The cleaning operation is effected and the remaining toner particles on the surface of fixing roller 13 are effectively removed by cleaning pad 47 at the second position. The pair of inner projections 39a and 39b, the pair of short projections 43a and 43b, the slanted surface of cleaning pad 47 and the rotation of fixing roller 13 act as a loading means, which moves cleaning pad 47 to a cleaning position (second position) when fixing roller 13 is driven. With the above-described embodiment, cleaning pad 47 is pressed on the surface of fixing roller 13 by a sufficient force (elastic restoring force) at the second position without the use of external urging means such as a leaf spring, and thus, the toner particle remaining on the surface of fixing roller 13 is removed smoothly. Since cleaning pad 47 is in contact with a portion of the surface of fixing roller 13 lower than the upper-most portion of fixing roller 13 because of its construction feature, an overall height of fixing device 35 may be lowered. In addition, since cleaning pad 47 is loaded only while fixing roller 13 is rotated, the excessive deformation of cleaning pad 47 is avoided during the service period, and thus a service life of cleaning pad 47 is extended. In the above-described embodiment, the pair of short projections 43a and 43b is formed on holder 45 and the pair of inner projections 39a and 39b is formed on frame 39. As shown in FIGURE 8, however, holder 45 may be provided with a short projection 61 at the rear wall portion, instead of the pair of short projections 43a and 43b, and frame 39 may be provided with a depression 63, instead of the pair of inner projections 39a and 39b, to be engaged with short projection 61. In the embodiment shown in Figure 8, components which correspond to those used in the embodiment of Figures 2 to 7 have been given the same reference numerals, and detailed description of those components has not been repeated. In the fixing device according to the invention, external urging means such as a leaf spring is not required, so that an overall height of the fixing device is reduced when compared with conventional fixing devices, and the service life of the cleaning pad is also increased. The invention has been described with reference to two specific embodiments but various modifications will be obvious to those skilled in the art which do not depart from the scope of the invention, as defined by the appendant claims.

Claims: A fixing device (35) which receives a medium (P) on which a toner image is supported, comprising: a frame (39); an elongated fixing roller (13) rotatably supported by the frame (39); an elongate pressure roller (15) rotatably supported by the frame (39) and forcibly engaged with the fixing roller (13) to carry out a fixing operation in which the toner on the medium (P) is fixed; an elongate cleaning holder (45) detachably located in the frame (39); and a compressible cleaning pad (47) supported by the holder (45), characterised in that: one elongated surface of the holder is inclined with respect to the horizontal elongated surface of the holder; in that the cleaning pad (47) is supported by the inclined surface of the holder (45), such that the surface of the cleaning pad (47) is in contact with a portion of the surface of the fixing roller (13) at a first position offset from the position on the surface of the fixing roller intersected by a vertical line (VL) passing through the rotational centre (13r) of the fixing roller (13); and in that loading means are provided for performing an engagement of the cleaning holder (45) and the frame (39) only when said fixing roller (13) is rotated during a fixing operation such that the holder (45) is located at a position in the frame (39) in which the cleaning pad (47) is moved to a cleaning position where it is forcibly compressed against the surface of the fixing roller (13) at said second cleaning position. A device according to claim 1, wherein the loading means includes a pair of projections (43a, 43b) respectively formed at opposite elongated ends (45a, 45b) of the holder (45) and the frame (39) includes a pair of engaging portions (39a, 39b) corresponding to the pair of projections (43a, 43b). A device according to claim 2, wherein the cleaning holder (45) includes means (51) for loosely maintaining the engagement of the cleaning holder (45) and the frame (39) while the fixing roller (13) is not rotated. A device according to claim 3, wherein the maintaining means includes a leaf plate (51) one end of which is fixed to one of the elongated ends (45a) of the holder (45) so that the holder (45) is urged in the elongated direction by the leaf plate (51) when the holder is located in the frame (39). A device according to claim 1, wherein the loading means includes a projection (61) at a side of the holder (45) perpendicular to the elongated direction of the holder (45) and a corresponding engaging portion (63) of the frame. An electrographic image forming apparatus comprising: image forming means (33) for forming a toner image on a medium (P); a frame (39); an elongated fixing roller (13) rotatably supported by the frame (39); an elongated pressure roller (15) rotatably supported by the frame and forcibly engaged with the fixing roller (13) to carry out a fixing operation in which the toner image is fixed on the medium (P); an elongate cleaning holder (45) detachably inserted in the frame (39); and a compressible cleaning pad (47) supported by the holder (45) detachably inserted in the frame (39), characterised in that one elongated surface of the holder (45) is inclined with respect to the horizontal elongated surface of the holder (45), and in that the cleaning pad (47) is supported by the inclined surface of the holder (45) so that the surface of the cleaning pad (47) is in contact with a portion of the surface (13b) of the fixing roller (13) at a first position offset from the position on the surface of the fixing roller intersected by a vertical line (VL) passing through the rotational centre (13r) of the fixing roller (13), and in that loading means are provided for performing an engagement of the cleaning holder (45) and the frame (39) only when said fixing roller (13) is rotated during a fixing operation such that the holder (45) is located at a position in the frame (39) in which the cleaning pad (47) is moved to a cleaning position in which it is forcibly compressed against the surface of the fixing roller (13) at said second cleaning position.

Inventors: ISHIGURO TOSHITSUGU, ISHIGURO, TOSHITSUGU, ISHIGURO, TOSHITSUGU, C/O INTELLECTUAL PTY DIV.
Applicants: TOKYO ELECTRIC CO LTD, TOKYO DENKI KABUSHIKI KAISHA
Application year: 1994
Main classification: G03G15
IPC codes: G03G15